185 research outputs found
Distribution of Glycerol Dialkyl Glycerol Tetraethers (GDGTs) in Microbial Mats From Holocene and Miocene Sabkha Sediments
Sabkhas are important settings for understanding early earth biological environments,
and the algal mats associated with them are thought to be potential source rocks for
hydrocarbon production. In this study we compare the sedimentological facies and
distribution of branched, and isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs)
in modern and mid-Holocene sabkha sediments from Abu Dhabi with well-preserved
Miocene (12β13 Ma) sabkha sediments recently recovered at IODP site U1464 off
the north coast of Australia. We show that the facies of the Miocene sediments is
very similar to Holocene and modern sabkhas. Furthermore, we show that there are
distinct patterns of isoprenoid GDGT distributions in the modern sabkha and that
these patterns are well preserved in both the buried Holocene and the Miocene
algal mats. The sabkha sediments analyzed are characterized by high %GDGT-0 and
methane index, dominance of branched GDGTs over crenarchaeol (high BIT index), an
unusual distribution of isoprenoid GDGTs 1β3, and also low abundance of archeol. The
distribution of branched GDGT differs between modern and Miocene sabkhas and
is similar in Miocene sabkha and non-sabkha sediments suggesting that they may
be of limited use to distinguish paleo-sabkha sediments. Overall, isoprenoid GDGT
distributions appear to be different from those found in modern soils, lakes and marine
sediments, as well as from those found in Miocene shallow water sediments right below
the sabkha, therefore they could be used in combination with facies analysis to identify
paleo-sabkha environments in sedimentary sequences
ΠΡΠΈΡΠ΅ΡΠΈΠΈ ΠΈ ΡΡΠ΅Π΄ΡΡΠ²Π° ΡΠ°Π·Π²ΠΈΡΠΈΡ ΠΏΡΠΎΠ³ΡΠ°ΠΌΠΌΠ½ΠΎΠ³ΠΎ ΠΎΠ±Π΅ΡΠΏΠ΅ΡΠ΅Π½ΠΈΡ Π΄Π»Ρ ΠΌΠΎΠ΄Π΅Π»ΠΈΡΠΎΠ²Π°Π½ΠΈΡ Π½Π΅ΡΡΠ΅Π³Π°Π·ΠΎΠ²ΡΡ ΠΌΠ΅ΡΡΠΎΡΠΎΠΆΠ΄Π΅Π½ΠΈΠΉ
ΠΠ±ΡΡΠΆΠ΄Π°ΡΡΡΡ ΡΠ΅Π·ΡΠ»ΡΡΠ°ΡΡ Π°Π½Π°Π»ΠΈΠ·Π° ΠΏΡΠΈΠΌΠ΅Π½ΠΈΠΌΠΎΡΡΠΈ ΠΈ ΡΡΡΠ΅ΠΊΡΠΈΠ²Π½ΠΎΡΡΠΈ ΠΏΡΠΎΠ³ΡΠ°ΠΌΠΌΠ½ΡΡ
ΡΠΈΡΡΠ΅ΠΌ Π²Π΅Π΄ΡΡΠΈΡ
Π·Π°ΡΡΠ±Π΅ΠΆΠ½ΡΡ
ΠΈ ΠΎΡΠ΅ΡΠ΅ΡΡΠ²Π΅Π½Π½ΡΡ
ΠΏΡΠΎΠΈΠ·Π²ΠΎΠ΄ΠΈΡΠ΅Π»Π΅ΠΉ, ΠΊΡΠ»ΡΡΠΈΠ²ΠΈΡΡΠ΅ΠΌΡΡ
Π½Π° ΡΡΠ½ΠΊΠ΅ ΠΈΠ½ΡΠΎΡΠΌΠ°ΡΠΈΠΎΠ½Π½ΡΡ
ΡΠ΅Ρ
Π½ΠΎΠ»ΠΎΠ³ΠΈΠΉ Π΄Π»Ρ ΠΌΠΎΠ΄Π΅Π»ΠΈΡΠΎΠ²Π°Π½ΠΈΡ Π½Π΅ΡΡΠ΅Π³Π°Π·ΠΎΠ²ΡΡ
ΠΌΠ΅ΡΡΠΎΡΠΎΠΆΠ΄Π΅Π½ΠΈΠΉ. Π‘ΡΠΎΡΠΌΡΠ»ΠΈΡΠΎΠ²Π°Π½Ρ ΠΊΡΠΈΡΠ΅ΡΠΈΠΈ ΠΎΡΠ΅Π½ΠΊΠΈ Π±Π°Π·ΠΎΠ²ΡΡ
ΠΏΡΠΎΠ³ΡΠ°ΠΌΠΌΠ½ΡΡ
ΡΠΈΡΡΠ΅ΠΌ, ΠΊΠΎΡΠΎΡΡΠΌΠΈ ΡΠ»Π΅Π΄ΡΠ΅Ρ ΡΡΠΊΠΎΠ²ΠΎΠ΄ΡΡΠ²ΠΎΠ²Π°ΡΡΡΡ ΠΏΡΠΈ ΠΎΠ±ΠΎΡΠ½ΠΎΠ²Π°Π½ΠΈΠΈ Π²ΡΠ±ΠΎΡΠ°. ΠΠ°Π½ΠΎ ΡΠΎΡΠΌΠ°Π»ΠΈΠ·ΠΎΠ²Π°Π½Π½ΠΎΠ΅ ΠΎΠΏΠΈΡΠ°Π½ΠΈΠ΅ ΡΠ»ΠΎΠΆΠ½ΡΡ
ΠΏΡΠΎΡΠ΅ΡΡΠΎΠ² Π³Π΅ΠΎΠ»ΠΎΠ³ΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ ΠΈ Π³ΠΈΠ΄ΡΠΎΠ΄ΠΈΠ½Π°ΠΌΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ ΠΌΠΎΠ΄Π΅Π»ΠΈΡΠΎΠ²Π°Π½ΠΈΡ Π½Π΅ΡΡΠ΅Π³Π°Π·ΠΎΠ²ΡΡ
ΠΌΠ΅ΡΡΠΎΡΠΎΠΆΠ΄Π΅Π½ΠΈΠΉ Ρ ΠΈΡΠΏΠΎΠ»ΡΠ·ΠΎΠ²Π°Π½ΠΈΠ΅ΠΌ ΡΠΈΡΡΠΎΠ²ΡΡ
3D-ΠΌΠΎΠ΄Π΅Π»Π΅ΠΉ ΠΈ ΠΏΠΎΠ΄Π΄Π΅ΡΠΆΠΈΠ²Π°ΡΡΠΈΡ
ΠΈΡ
ΠΏΡΠΎΠ³ΡΠ°ΠΌΠΌΠ½ΡΡ
ΡΠΈΡΡΠ΅ΠΌ
ΠΠ½Π°Π»ΠΈΠ· ΠΈ ΠΈΠ½ΡΠ΅ΡΠΏΡΠ΅ΡΠ°ΡΠΈΡ Π³ΠΈΠ΄ΡΠΎΠ΄ΠΈΠ½Π°ΠΌΠΈΡΠ΅ΡΠΊΠΈΡ ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½ΠΈΠΉ Π΄Π»Ρ Π΄Π²ΡΡ ΡΠ°Π·Π½ΠΎΠ³ΠΎ ΠΏΠΎΡΠΎΠΊΠ° (Π²ΠΎΠ΄Π°-Π½Π΅ΡΡΡ)
ΠΠΎΠΊΠ°Π·Π°Π½Ρ ΠΏΡΠΎΠ±Π»Π΅ΠΌΡ, Π²ΠΎΠ·Π½ΠΈΠΊΠ°ΡΡΠΈΠ΅ ΠΏΡΠΈ ΠΈΠ½ΡΠ΅ΡΠΏΡΠ΅ΡΠ°ΡΠΈΠΈ ΠΈ Π°Π½Π°Π»ΠΈΠ·Π΅ Π΄Π°Π½Π½ΡΡ
Π³ΠΈΠ΄ΡΠΎΠ΄ΠΈΠ½Π°ΠΌΠΈΡΠ΅ΡΠΊΠΈΡ
ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½ΠΈΠΉ, ΠΏΡΠΎΠ²Π΅Π΄Π΅Π½Π½ΡΡ
Π½Π° ΡΠΊΠ²Π°ΠΆΠΈΠ½Π°Ρ
Ρ ΠΎΠ±Π²ΠΎΠ΄Π½Π΅Π½Π½ΠΎΡΡΡΡ, ΠΎΡΠ»ΠΈΡΠ½ΠΎΠΉ ΠΎΡ Π½ΡΠ»Ρ. Π Π°Π·ΠΎΠ±ΡΠ°Π½Ρ ΠΏΡΠ΅ΠΈΠΌΡΡΠ΅ΡΡΠ²Π° ΠΈ Π½Π΅Π΄ΠΎΡΡΠ°ΡΠΊΠΈ ΠΏΡΠΈΠΌΠ΅Π½ΡΠ΅ΠΌΡΡ
ΠΌΠ΅ΡΠΎΠ΄ΠΎΠ² ΠΈΠ½ΡΠ΅ΡΠΏΡΠ΅ΡΠ°ΡΠΈΠΈ ΠΈ Π°Π½Π°Π»ΠΈΠ·Π°. ΠΡΠ΅Π΄ΡΡΠ°Π²Π»Π΅Π½ Π½ΠΎΠ²ΡΠΉ ΠΌΠ΅ΡΠΎΠ΄ Π½ΠΎΡΠΌΠ°Π»ΠΈΠ·Π°ΡΠΈΠΈ ΠΏΠΎΠ΄Π²ΠΈΠΆΠ½ΠΎΡΡΠΈ Π΄Π»Ρ Π°Π½Π°Π»ΠΈΠ·Π° ΡΠ΅Π·ΡΠ»ΡΡΠ°ΡΠΎΠ² Π³ΠΈΠ΄ΡΠΎΠ΄ΠΈΠ½Π°ΠΌΠΈΡΠ΅ΡΠΊΠΈΡ
ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½ΠΈΠΉ ΡΠΊΠ²Π°ΠΆΠΈΠ½
ΠΠ»Π΅ΠΊΡΡΠΎΠΎΡΠ°ΠΆΠ΄Π΅Π½ΠΈΠ΅ ΡΠΏΠ»Π°Π²Π° ΡΠ²ΠΈΠ½Π΅Ρ-ΠΎΠ»ΠΎΠ²ΠΎ ΠΈΠ· ΠΌΠ΅ΡΠ°Π½ΡΡΠ»ΡΡΠΎΠ½Π°ΡΠ½ΡΡ ΡΠ°ΡΡΠ²ΠΎΡΠΎΠ²
ΠΠΎΡΠ»ΡΠ΄ΠΆΠ΅Π½ΠΎ Π²ΠΏΠ»ΠΈΠ² ΡΡΠ·Π½ΠΈΡ
ΡΠΈΠ½Π½ΠΈΠΊΡΠ² Π½Π° ΡΠΊΠ»Π°Π΄ ΡΠΏΠ»Π°Π²Ρ ΡΠ²ΠΈΠ½Π΅ΡΡ-ΠΎΠ»ΠΎΠ²ΠΎ, ΡΠΎ ΠΎΡΠ°Π΄ΠΆΠ΅Π½ΠΈΠΉ Π· Π΅Π»Π΅ΠΊΡΡΠΎΠ»ΡΡΡ Π½Π° ΠΎΡΠ½ΠΎΠ²Ρ ΠΌΠ΅ΡΠ°Π½ΡΡΠ»ΡΡΠΎΠ½Π°ΡΠ½ΠΎΡ ΠΊΠΈΡΠ»ΠΎΡΠΈ. ΠΠ΅ΡΠΎΠ΄ΠΎΠΌ ΠΏΠΎΠ²Π½ΠΎΠ³ΠΎ ΡΠ°ΠΊΡΠΎΡΠ½ΠΎΠ³ΠΎ Π΅ΠΊΡΠΏΠ΅ΡΠΈΠΌΠ΅Π½ΡΡ ΠΠ€Π2Β³ ΠΎΡΡΠΈΠΌΠ°Π½Ρ ΡΡΠ²Π½ΡΠ½Π½Ρ ΡΠ΅Π³ΡΠ΅ΡΡΡ, ΡΠΎ Π°Π΄Π΅ΠΊΠ²Π°ΡΠ½ΠΎ ΠΎΠΏΠΈΡΡΡΡΡ Π·Π°Π»Π΅ΠΆΠ½ΡΡΡΡ Π²ΠΌΡΡΡΡ ΠΎΠ»ΠΎΠ²Π° Π² ΡΠΏΠ»Π°Π²Ρ Π²ΡΠ΄ ΡΠΌΠΎΠ² ΠΎΡΠ°Π΄ΠΆΠ΅Π½Π½Ρ Π· Π΅Π»Π΅ΠΊΡΡΠΎΠ»ΡΡΡΠ² ΡΠ· ΠΎΡΠ³Π°Π½ΡΡΠ½ΠΈΠΌΠΈ Π΄ΠΎΠ±Π°Π²ΠΊΠ°ΠΌΠΈ Ρ Π±Π΅Π· Π½ΠΈΡ
.Effect of different factors on content of lead-tin alloys obtained from an electrolyte on the base of methanesulfonic acid is investigated. The method of full factor experiment FFE 2Β³ is used for obtaining of regression equations which adequately describe the relation between the electrodeposition condition and the contents of tin in alloys from electrolytes with and without some organic additives
Nano- to Millimeter Scale Morphology of Connected and Isolated Porosity in the Permo-Triassic Khuff Formation of Oman
Carbonate reservoirs form important exploration targets for the oil and gas industry in
many parts of the world. This study aims to differentiate and quantify pore types and their relation to
petrophysical properties in the Permo-Triassic Khuff Formation, a major carbonate reservoir in Oman.
For that purpose, we have employed a number of laboratory techniques to test their applicability for
the characterization of respective rock types. Consequently, a workflow has been established utilizing
a combined analysis of petrographic and petrophysical methods which provide the best results for
pore-system characterization. Micro-computed tomography (ΞΌCT) analysis allows a representative
3D assessment of total porosity, pore connectivity, and effective porosity of the ooid-shoal facies but it
cannot resolve the full pore-size spectrum of the highly microporous mud-/wackestone facies. In order
to resolve the smallest pores, combined mercury injection capillary pressure (MICP), nuclear magnetic
resonance (NMR), and BIB (broad ion beam)-SEM analyses allow covering a large pore size range
from millimeter to nanometer scale. Combining these techniques, three different rock types with
clearly discernible pore networks can be defined. Moldic porosity in combination with intercrystalline
porosity results in the highest effective porosities and permeabilities in shoal facies. In back-shoal
facies, dolomitization leads to low total porosity but well-connected and heterogeneously distributed
vuggy and intercrystalline pores which improves permeability. Micro- and nanopores are present
in all analyzed samples but their contribution to effective porosity depends on the textural context.
Our results confirm that each individual rock type requires the application of appropriate laboratory
techniques. Additionally, we observe a strong correlation between the inverse formation resistivity
factor and permeability suggesting that pore connectivity is the dominating factor for permeability
but not pore size. In the future, this relationship should be further investigated as it could potentially
be used to predict permeability from wireline resistivity measured in the flushed zone close to the
borehole wall
Recommended from our members
Nano- to millimeter scale morphology of connected and isolated porosity in the permo-triassic khuff formation of Oman
Carbonate reservoirs form important exploration targets for the oil and gas industry in many parts of the world. This study aims to differentiate and quantify pore types and their relation to petrophysical properties in the Permo-Triassic Khuff Formation, a major carbonate reservoir in Oman. For that purpose, we have employed a number of laboratory techniques to test their applicability for the characterization of respective rock types. Consequently, a workflow has been established utilizing a combined analysis of petrographic and petrophysical methods which provide the best results for pore-system characterization. Micro-computed tomography (ΞΌCT) analysis allows a representative 3D assessment of total porosity, pore connectivity, and effective porosity of the ooid-shoal facies but it cannot resolve the full pore-size spectrum of the highly microporous mud-/wackestone facies. In order to resolve the smallest pores, combined mercury injection capillary pressure (MICP), nuclear magnetic resonance (NMR), and BIB (broad ion beam)-SEM analyses allow covering a large pore size range from millimeter to nanometer scale. Combining these techniques, three different rock types with clearly discernible pore networks can be defined. Moldic porosity in combination with intercrystalline porosity results in the highest effective porosities and permeabilities in shoal facies. In back-shoal facies, dolomitization leads to low total porosity but well-connected and heterogeneously distributed vuggy and intercrystalline pores which improves permeability. Micro- and nanopores are present in all analyzed samples but their contribution to effective porosity depends on the textural context. Our results confirm that each individual rock type requires the application of appropriate laboratory techniques. Additionally, we observe a strong correlation between the inverse formation resistivity factor and permeability suggesting that pore connectivity is the dominating factor for permeability but not pore size. In the future, this relationship should be further investigated as it could potentially be used to predict permeability from wireline resistivity measured in the flushed zone close to the borehole wall. Β© 2019 by the authors. Licensee MDPI, Basel, Switzerland
ΠΠ΅Π½ΡΠΈΠ»ΡΡΠΈΡ ΡΠ°Ρ Ρ ΠΈ ΡΡΠ΄Π½ΠΈΠΊΠΎΠ²
Π Π°ΡΡΠΌΠΎΡΡΠ΅Π½Ρ ΡΡΡΡΠΊΡΡΡΠ° ΠΈ ΠΎΡΠ½ΠΎΠ²Π½ΡΠ΅ ΡΠ»Π΅ΠΌΠ΅Π½ΡΡ ΡΠ°Ρ
ΡΠ½ΡΡ
Π²Π΅Π½ΡΠΈΠ»ΡΡΠΈΠΎΠ½Π½ΡΡ
ΡΠΈΡΡΠ΅ΠΌ, ΡΠΏΠΎΡΠΎΠ±Ρ ΠΈ ΡΡ
Π΅ΠΌΡ ΠΏΡΠΎΠ²Π΅ΡΡΠΈΠ²Π°Π½ΠΈΡ ΡΠ°Ρ
Ρ, ΡΡΠ΄Π½ΠΈΠΊΠΎΠ², ΠΊΠ°ΡΡΠ΅ΡΠΎΠ², Π²Π΅Π½ΡΠΈΠ»ΡΡΠΈΠΈ
Π²ΡΠ΅ΠΌΠΎΡΠ½ΡΡ
ΡΡΠ°ΡΡΠΊΠΎΠ² ΠΈ ΡΡΠΏΠΈΠΊΠΎΠ²ΡΡ
Π²ΡΡΠ°Π±ΠΎΡΠΎΠΊ. ΠΠ°ΡΡΠΎΠ½ΡΡΡ, ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½Ρ Π²ΠΎΠΏΡΠΎΡΡ
ΠΎΠ±ΠΎΡΠ½ΠΎΠ²Π°Π½ΠΈΡ ΠΈ Π²ΡΠ±ΠΎΡΠ° ΠΏΠ°ΡΠ°ΠΌΠ΅ΡΡΠΎΠ² ΡΠΈΡΡΠ΅ΠΌ Π²Π΅Π½ΡΠΈΠ»ΡΡΠΈΠΈ, Ρ
Π°ΡΠ°ΠΊΡΠ΅ΡΠΈΡΡΠΈΠΊ ΡΠ΅Ρ
Π½ΠΈΡΠ΅ΡΠΊΠΈΡ
ΡΡΠ΅Π΄ΡΡΠ², ΠΎΠ±Π΅ΡΠΏΠ΅ΡΠΈΠ²Π°ΡΡΠΈΡ
ΠΈΡ
ΡΠ°ΡΡΠ΅ΡΠ½ΡΠ΅ Π·Π½Π°ΡΠ΅Π½ΠΈΡ ΠΏΠ°ΡΠ°ΠΌΠ΅ΡΡΠΎΠ² ΡΠΈΡΡΠ΅ΠΌ Π²Π΅Π½ΡΠΈΠ»ΡΡΠΈΠΈ.
ΠΠΎΡΠΎΠ±ΠΈΠ΅ ΡΠΎΠΎΡΠ²Π΅ΡΡΡΠ²ΡΠ΅Ρ ΠΏΡΠΎΠ³ΡΠ°ΠΌΠΌΠ΅ ΠΊΡΡΡΠ° Β«ΠΠ΅Π½ΡΠΈΠ»ΡΡΠΈΡ ΡΠ°Ρ
Ρ ΠΈ ΡΡΠ΄Π½ΠΈΠΊΠΎΠ²Β» Π΄Π»Ρ
ΡΡΡΠ΄Π΅Π½ΡΠΎΠ² ΡΠΏΠ΅ΡΠΈΠ°Π»ΡΠ½ΠΎΡΡΠΈ Β«Π Π°Π·ΡΠ°Π±ΠΎΡΠΊΠ° ΠΌΠ΅ΡΡΠΎΡΠΎΠΆΠ΄Π΅Π½ΠΈΠΉ ΠΈ Π΄ΠΎΠ±ΡΡΠ° ΠΏΠΎΠ»Π΅Π·Π½ΡΡ
ΠΈΡΠΊΠΎΠΏΠ°Π΅ΠΌΡΡ
Β» ΠΈ ΠΌΠΎΠΆΠ΅Ρ Π±ΡΡΡ ΠΈΡΠΏΠΎΠ»ΡΠ·ΠΎΠ²Π°Π½ΠΎ ΠΏΡΠΈ ΠΏΠΎΠ΄Π³ΠΎΡΠΎΠ²ΠΊΠ΅ ΠΈ ΠΏΠΎΠ²ΡΡΠ΅Π½ΠΈΠΈ
ΠΊΠ²Π°Π»ΠΈΡΠΈΠΊΠ°ΡΠΈΠΈ ΠΈΠ½ΠΆΠ΅Π½Π΅ΡΠ½ΠΎ-ΡΠ΅Ρ
Π½ΠΈΡΠ΅ΡΠΊΠΈΡ
ΡΠ°Π±ΠΎΡΠ½ΠΈΠΊΠΎΠ² Π³ΠΎΡΠ½ΡΡ
ΠΏΡΠ΅Π΄ΠΏΡΠΈΡΡΠΈΠΉ, Π° ΡΠ°ΠΊΠΆΠ΅
ΡΡΡΠ΄Π΅Π½ΡΠ°ΠΌΠΈ Π΄ΡΡΠ³ΠΈΡ
ΡΠΏΠ΅ΡΠΈΠ°Π»ΡΠ½ΠΎΡΡΠ΅ΠΉ, ΠΎΠ±ΡΡΠ°ΡΡΠΈΡ
ΡΡ ΠΏΠΎ Π½Π°ΠΏΡΠ°Π²Π»Π΅Π½ΠΈΡ Β«ΠΠΎΡΠ½ΠΎΠ΅ Π΄Π΅Π»ΠΎΒ»
Two-dimensional X-ray diffraction as a tool for the rapid, non-destructive detection of low calcite quantities in aragonitic corals
Paleoclimate reconstructions based on reef corals require precise detection of diagenetic alteration. Secondary calcite can significantly affect paleotemperature reconstructions at very low amounts of ~1%. X-ray powder diffraction is routinely used to detect diagenetic calcite in aragonitic corals. This procedure has its limitations as single powder samples might not represent the entire coral heterogeneity. A conventional and a 2-D X-ray diffractometer were calibrated with gravimetric powder standards of high and low magnesium calcite (0.3% to 25% calcite). Calcite contentsβ<1% can be recognized with both diffractometer setups based on the peak area of the calcite [104] reflection. An advantage of 2-D-XRD over convenient 1-D-XRD methods is the nondestructive and rapid detection of calcite with relatively high spatial resolution directly on coral slabs. The calcite detection performance of the 2-D-XRD setup was tested on thin sections from fossil Porites sp. samples that, based on powder XRD measurements, showed <1% calcite. Quantification of calcite contents for these thin sections based on 2-D-XRD and digital image analysis showed very similar results. This enables spot measurements with diameters of βΌ4 mm, as well as systematic line scans along potential tracks previous to geochemical proxy sampling. In this way, areas affected by diagenetic calcite can be avoided and alternative sampling tracks can be defined. Alternatively, individual sampling positions that show dubious proxy results can later be checked for the presence of calcite. The presented calibration and quantification method can be transferred to any 2-D X-ray diffractometer
Modern and sub-fossil corals suggest reduced temperature variability in the eastern pole of the Indian Ocean Dipole during the medieval climate anomaly
We present two 40 year records of monthly coral Sr/Ca ratios from the eastern pole of the Indian Ocean Dipole. A modern coral covers the period from 1968 to 2007. A sub-fossil coral derives from the medieval climate anomaly (MCA) and spans 1100β1140 ad. The modern coral records SST variability in the eastern pole of the Indian Ocean Dipole. A strong correlation is also found between coral Sr/Ca and the IOD index. The correlation with ENSO is asymmetric: the coral shows a moderate correlation with El NiΓ±o and a weak correlation with La NiΓ±a. The modern coral shows large interannual variability. Extreme IOD events cause coolingβ>β3 Β°C (1994, 1997) orβ~β2 Β°C (2006). In total, the modern coral indicates 32 warm/cool events, with 16 cool and 16 warm events. The MCA coral shows 24 warm/cool events, with 14 cool and 10 warm events. Only one cool event could be comparable to the positive Indian Ocean Dipole in 2006. The seasonal cycle of the MCA coral is reduced (<β50% of to the modern) and the skewness of the Sr/Ca data is lower. This suggests a deeper thermocline in the eastern Indian Ocean associated with a La NiΓ±a-like mean state in the Indo-Pacific during the MCA
Indonesian Throughflow drove Australian climate from humid Pliocene to arid Pleistocene
Late Miocene to mid-Pleistocene sedimentary proxy records reveal that northwest Australia underwent an abrupt transition from dry to humid climate conditions at 5.5 million years (Ma), likely receiving year-round rainfall, but after ~3.3 Ma, climate shifted toward an increasingly seasonal precipitation regime. The progressive constriction of the Indonesian Throughflow likely decreased continental humidity and transferred control of northwest Australian climate from the Pacific to the Indian Ocean, leading to drier conditions punctuated by monsoonal precipitation. The northwest dust pathway and fully established seasonal and orbitally controlled precipitation were in place by ~2.4 Ma, well after the intensification of Northern Hemisphere glaciation. The transition from humid to arid conditions was driven by changes in Pacific and Indian Ocean circulation and regional atmospheric moisture transport, influenced by the emerging Maritime Continent. We conclude that the Maritime Continent is the switchboard modulating teleconnections between tropical and high-latitude climate systems
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